Associated type use triggers a bogus error message
In GHCi, version 6.11.20090115 built from HEAD
{-# LANGUAGE TypeOperators, TypeFamilies #-}
{-# OPTIONS_GHC -Wall #-}
-- With associate type synonym, the ch' definition leads to
--
-- Couldn't match expected type `Basis u1'
-- against inferred type `Basis u'
-- Expected type: u1 :-* v
-- Inferred type: u :-* v
-- In the expression: ch
-- In the definition of `ch'': ch' = ch
--
-- With associated data type, no problem.
class HasBasis u where type Basis u :: *
-- class HasBasis u where data Basis u :: *
type u :-* v = Basis u -> v
ch :: (HasBasis u, HasBasis v) =>
(v :-* w) -> (u :-* v) -> (u :-* w)
ch = undefined
ch' :: (HasBasis u, HasBasis v) =>
(v :-* w) -> (u :-* v) -> (u :-* w)
ch' = ch
Trac metadata
Trac field | Value |
---|---|
Version | 6.11 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | conal@conal.net |
Operating system | |
Architecture |